Field of the Invention
The present invention relates to optical sensors and, more particularly, to optical chemical or biochemical sensors for implantation within a living animal and measurement of a concentration of an analyte in a medium within the living animal.
Description of the Background
U.S. Pat. No. 5,517,313, which is incorporated herein by reference in its entirety, describes a fluorescence-based sensing device comprising indicator molecules and a photosensitive element, e.g., a photodetector. Broadly speaking, in the context of the field of the present invention, indicator molecules are molecules where one or more optical characteristics of which is or are affected by the local presence of an analyte. In the device according to U.S. Pat. No. 5,517,313, a light source, e.g., a light-emitting diode (“LED”), is located at least partially within a layer of material containing fluorescent indicator molecules or, alternatively, at least partially within a wave guide layer such that radiation (light) emitted by the source strikes and causes the indicator molecules to fluoresce. A high-pass filter allows fluorescent light emitted by the indicator molecules to reach the photosensitive element (photodetector) while filtering out scattered light from the light source.
The fluorescence of the indicator molecules employed in the device described in U.S. Pat. No. 5,517,313 is modulated, i.e., attenuated or enhanced, by the local presence of an analyte. For example, the orange-red fluorescence of the complex tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate is quenched by the local presence of oxygen. Therefore, this complex can be used advantageously as the indicator molecule in an oxygen sensor. Indicator molecules whose fluorescence properties are affected by various other analytes are known as well.
Furthermore, indicator molecules which absorb light, with the level of absorption being affected by the presence or concentration of an analyte, are also known. See, for example, U.S. Pat. No. 5,512,246, which is incorporated by reference in its entirety, which discloses compositions whose spectral responses are attenuated by the local presence of polyhydroxyl compounds such as sugars.
In the sensor described in U.S. Pat. No. 5,517,313, the material which contains the indicator molecules is permeable to the analyte. Thus, the analyte can diffuse into the material from the surrounding test medium, thereby affecting the fluorescence of the indicator molecules. The light source, indicator molecule-containing matrix material, high-pass filter, and photodetector are configured such that fluorescent light emitted by the indicator molecules impacts the photodetector such that an electrical signal is generated that is indicative of the concentration of the analyte in the surrounding medium.
The sensing device described in U.S. Pat. No. 5,517,313 represents a marked improvement over devices which constitute prior art with respect to U.S. Pat. No. 5,517,313. There has, however, remained a need for sensors that permit the detection of various analytes in the body of a living animal, e.g., a living human.
U.S. Pat. Nos. 6,330,464; 6,400,974; 6,711,423 and 7,308,292, which are incorporated herein by reference in their entireties, each describe a sensing device comprising indicator molecules and a photosensitive element that is designed for use in the human body. Despite the advancements to the state of the art represented by the sensing devices described in these patents, there still a desire for improved sensing devices.